1. Field of the Invention
The invention relates to vibration damping devices and is directed more particularly to a flexible electrorheological (ER) vibration damping device.
2. Description of the Prior Art
A predominant method for the dissipation of vibrational energy is through the interaction between a plunger mechanism and a fluid in an enclosed chamber. The proficiency of such dampers is dependent, at least in part, on the viscosity of the fluid, the pressure under which the fluid is maintained, and the like. Once selected, the viscosity is fixed unless and until the fluid is removed and replaced by a fluid having a different viscosity. Such dampers typically are provided with moving parts which include, in addition to a moving piston, mechanical linkages, valves, and orifices. If the fluid chamber forms part of a hydraulic system, all the appurtenances of a hydraulic system are required, including pumps, regulators, and the like.
The discovery of electrorheological (ER) fluids in 1940, made available fluids adapted to transform from a Newtonian fluid to a solid substance, capable of resisting an applied stress, when the fluid is activated by an electrical potential. When the electric potential is removed, the solid substance reverts to the original Newtonian fluid. ER fluids are two-phase systems containing micron sized particles suspended in a carrier fluid. When the ER fluid is subjected to an electric field, the particles polarize and develop a network of three dimensional chains. The ER fluids develop an electric field dependent yield stress, when activated by an electric field. In the activated state, the ER fluids resist an applied shear stress, providing the applied load does not exceed the developed yield stress. In the absence of an electric field, an ER fluid exhibits Newtonian behavior. The activation time from the Newtonian state to the stress resistant state is typically on the order of a few milliseconds. The many applications of such fluids includes use in clutches, viscous dampers, valves and active engine mounts.
There have been developed systems for the dissipation of vibrational energy through the interaction between a plunger mechanism and the ER fluid. The ER fluid properties are actively altered by the magnitude of an electric field applied; thus, the response of the structure is readily altered and controlled. One such device, shown in FIG. 1, utilizes vanes 10 affixed to the damper's plunger 12. The attached vanes 10 are spaced from the surface of copper plates 14 lining the inside surface of a damper casing 16. When copper plates 14 are energized, the volume of ER fluid between vanes 10 and copper plates 14 is activated, or electrically stressed, thereby placing that portion of the ER fluid in a stress-resistant state. As plunger 12 moves up and down inside casing 16, the ER fluid along with the copper plates 14 is successively and repeatedly activated and deactivated by the motion of the vanes 10.
In another such device, shown in FIG. 2, an orifice 20 between upper and lower fluid chambers (22, 24) includes an electrode structure. Plates 26 of the electrode structure are parallel to the direction of fluid flow through orifice 20. The activation and deactivation of the ER fluid controls the amount of fluid which can flow through orifice 20.